Search

Enantioselective hydrolysis of epoxides by epoxide hydrolase (EH) is one of the most attractive approaches for the synthesis of chiral epoxides. So far, attempts to develop an efficient epoxide hydrolase -mediated biotransformation have been limited by either the low activity or insufficient enantioselectivity of epoxide hydrolase. In this study, iterative saturation mutagenesis (ISM) of epoxide hydrolase from Agrobacterium radiobacter AD1 (ArEH) was performed for efficient production of (R)-epichlorohydrin. Six amino acid residues, I108, A110, D131, I133, T247, and G245, were selected for site saturation mutagenesis, and a sequential combination of positive mutants using ISM was constructed. Targeted mutagenesis generated five mutants (T247K, I108L, D131S, T247K/I108L, and T247K/I108L/D131S) with improved activity and enantioselectivity. Kinetics analysis showed that the best mutant, T247K/I108L/D131S, exhibited a 4.5-fold higher catalytic efficiency (k cat/K m) value and a 2.1-fold higher enantioselectivity (E value) towards epichlorohydrin than the wild-type (WT) enzyme. Molecular docking computations support the source of notably improved enantioselectivity. In addition, the triple mutant also displayed a significantly enhanced thermostability, with > 8-fold longer half-life at 50 °C than WT. A gram-scale kinetic resolution of (R,S)-epichlorohydrin was performed using T247K/I108L/D131S mutant as biocatalyst, affording a (R)-epichlorohydrin yield of 40.2% (> 99.9% enantiomeric excess) and an average productivity of 1410 g L−1 d−1. The engineered T247K/I108L/D131S variant is a promising biocatalyst for the enzymatic synthesis of (R)-epichlorohydrin.

Salt severely restricts cotton (Gossypium hirsutum) growth and production. The present study was undertaken to study the effect of salt-induced hydrogen peroxide (H2O2) on antioxidant enzymes in cotton. NaCl treatment or exogenous H2O2 was used to investigate the relationship between H2O2 content and levels of antioxidant enzymes including superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), as well as the transcriptional levels of corresponding genes. H2O2 content increased within 24 h following 200 mmol L–1 NaCl treatment. Both NaCl-induced and exogenous H2O2 increased the activity of antioxidant enzymes including APX and SOD and upregulated the transcriptional levels of GhcAPX1, GhFeSOD, and GhchlCSD. These increased activities and upregulated transcriptional levels were inhibited when the salt-induced H2O2 was scavenged by NAC. These results indicate that salt-induced H2O2 as a second signaling messenger modulates APX and SOD activities by regulating the transcription levels of corresponding genes, alleviating oxidative stress, and increasing salt tolerance in cotton.

To improve the operational stability and reusability of an epoxide hydrolase (EH) for the biosynthesis of optically active epoxides. A covalently immobilization strategy was employed to improve the stability of Agrobacterium radiobacter EH by using ethylenediamine (EDA)-functionalised epoxy resin LX-1000EP as carrier. Under the optimal conditions, the activity recovery of immobilized enzyme was 72 % and the specific activity was 634 U/g. Immobilized EH exhibited significantly enhanced thermal stability with a half-life of more than 6.8-fold at 50 °C than that of the free enzyme. A gram-scale kinetic resolution of (R,S)-epichlorohydrin using immobilized preparation as biocatalyst was performed and (R)-epichlorohydrin was obtained with 35 % yield and 99 % enantiomeric excess. The immobilized EH showed good operational stability and even after six reactions, it retained >85 % of the initial activity. The operational stability and recyclability of immobilized EH on an EDA-functionalized epoxy supports demonstrated its potential for producing (R)-epichlorohydrin.

Carbon micro-spheres (CMSs) with diameters of several micrometers were synthesized by surfactant-assisted self-assembly of direct coal liquefaction products, which come from the lignite liquefaction with NaOH and methanol. The synthesized CMSs were characterized by X-ray diffraction, scanning electron microscope and TG analysis. The results show that cetyltrimethylammonium bromide (CTAB) and carbonization temperature play an important role in the formation of CMSs. The CMSs have a spherical morphology, smooth surface, probable size of about 5-10μm and a relatively high thermal resistance in N2 atmosphere. The formation mechanism of these CMSs was discussed based on the feature of the reaction system.

Nanodiamond powder (NDP) was dispersed in epoxy resin with low content by means of a high powerful ultrasonic liquid processor and then mixed with curing agent using a high-speed mechanical agitator. The good dispersion of NDP in epoxy could be observed. The mechanical properties of the NDP/epoxy nanocomposites were investigated. It was found that with a NDP content of only 0.3 wt%, the Vicker's hardness, tensile strength and tensile modulus of the NDP/epoxy nanocomposites were 24.7%, 52.7% and 54.2% higher than that of pure epoxy, respectively. The significant improvement of the mechanical properties of the NDP/epoxy nanocomposites could be attributed to the good dispersion of the NDP in the epoxy matrix and grafting of epoxy to NDP by an esterification reaction.

Shengfu (SF) coal was hydro-thermally treated with and without CaO addition at different temperatures and the crucible coking determinations were carried out to evaluate the effects. The results show that hydro-thermal treatment can obviously increase the micro-strength index (MSI) of the coke and particle coke strength after reaction (PSR), and decrease particle coke reactivity index (PRI), which are beneficial for metallurgical coke to increase the gas permeability in blast furnace. Addition of CaO during hydro-thermal treatment at 150-250°C greatly promotes the effects of hydro-thermal treatment. However, hydro-thermal treatment at 300°C with CaO results in dramatic decrease in MSI and PSR due to the enhanced hydrolysis reactions at this temperature by CaO to form strong cross-linking in the treated coal.

The hydrogenation of preasphaltene (PA), from Chinese Xiaolongtan lignite liquefied heavy product, was investigated with hydrogen storage materials in a batch autoclave. The effects of reaction conditions such as hydrogen storage materials and temperature on the yields of gas+oil, asphaltene, char and the conversions of preasphaltene were discussed. Preliminary studies indicate that increasing temperature not only improves hydrogen donor performance of hydrogen storage materials but also enhances conversion of feedstock PA and gas+oil yield. The conversion of PA and the yield gas+oil get to 72.02% and 41.46%, respectively, under 5% MgH2, 5MPa initial hydrogen pressure, temperature 420°C and reaction time 30min. Meanwhile MgH2 is stronger than NaBH4 in hydrodeoxygenation of PA under the same conditions. Elemental and FTIR analyses were used to illustrate the structural characteristics of feedstock PA and remaining preasphaltene (RPA).

In order to explore high-efficiency utilization approach of lignite, Xianfeng lignite was extracted by toluene/methanol (3:1) mixed solvent under 300°C in an autoclave combined with high-temperature separator. Subsequently, the thermal extraction residue was oxidized by 3% hydrogen peroxide aqueous solution at room temperature. The raw coal and its residues of thermal extraction and oxidization were further extracted respectively by THF and CS2/NMP mixed solvent, and the extracts and the extraction residues were characterized by FTIR. The results indicate that thermal extraction of lignite relaxes the network structure of coal matrix by disrupture the non-covalent bond interactions. The methylene bridge bond is easy to be oxidized into carboxyl and hydroxyl functional groups. Therefore, these results are very significant for the development of high-efficiency conversion technology.

A facile method to prepare PtRu/MWCNT nanocomposite with excellent electrocatalytic properties was reported in here. Highly dispersed bimetallic PtRu alloy catalysts have been supported on the ultrasonically treated MWCNTs by a rapid ultrasound induced HCHO reduction technique. The microstructure and nature of the resulting PtRu/MWCNT nanocomposite were characterized by Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The results demonstrated that the highly dispersed bimetallic PtRu alloy could be formed on the MWCNTs surface within 5 min at ambient temperature. The obtained PtRu/MWCNT electrode exhibits excellent electrocatalytic activity to methanol. The peak current of the 500th scan of PtRu-1 and E-TEK catalyst is about 75% and 70%, respectively, of that of the first scan. By contrast, for PtRu/MWCNT nanocomposite, after 500-cycle scans, its peak current still remains about 85%.

To understand the molecular and cellular mechanisms underlying the salt response and to isolate differentially expressed genes, we constructed a forward subtractive cDNA library from Salsola ferganica treated with 600 mM NaCl for different lengths of time (0, 4, 8, 12, 16, 24, 36 h) using the suppression subtractive hybridization (SSH) technique. This SSH library contained approximately 2,200 positive clones, with the insert size ranging from 250 to 700 bp. Eighty clones were selected for further study based on results from reverse Northern blotting and sequencing and, these cDNAs are the first reported expressed sequence tags (ESTs) of Salsola ferganica listed in GenBank. Among these 80 differentially expressed genes, 32 are genes with known function that display a high homology (between 68 and 100% identity) to known sequences, 47 have an unknown function, showing no homology with known sequences, and one is a novel gene that does not match any previously reported genes. Five cDNA fragments, sf3d8, sf6d8, sf4a8, sf8d6, and sf6c7, were randomly chosen from the 80 differentially expressed genes for reverse transcription-PCR analysis. The expression of sf8d6 was entirely induced by salt stress and that of sf3d8, sf6d8, sf4a8, and sf6c7 was increased from a relatively lower level. The isolated ESTs reported here may enable us to find new genes involved in salt tolerance in Salsola ferganica.

The liquefaction properties and mechanism of Xiaolongtan (XLT) lignite were studied. On the basis of high content of water in lignite, the liquefaction behavior of XLT lignite under different atmospheres using water as solvent was preliminarily probed. The results show that XLT lignite has a good liquefaction activity, and its liquefaction conversion gets to 94.5% at 420°C, H 2 atmosphere, and tetralin (THN) used as solvent. During coal liquefaction, the active H stabilizing free radicals formed during coal pyrolysis is mainly from hydrogen donor solvent. H 2 Gas has no hydrogenation activity, and it cannot directly provide active H for coal liquefaction. When water was used as solvent instead of THN in liquefaction of XLT lignite, high liquefaction conversion occurs under CO atmosphere compared to H 2 or N 2 atmosphere. This suggested that the water gas shift reaction produced active H under CO atmosphere. The active H stabilized the free radicals formed from coal pyrolysis to form lower molecular weight liquefaction products, and therefore, increasing liquefaction conversion. Because of the low primary pressure of CO in the experiment, the active H formed from the water gas shift reaction is limited. Thus, the liquefaction conversion of XLT lignite is not high when water is used as solvent. But our preliminary study shows that it is new lignite liquefaction technology using water as solvent under CO atmosphere and has remarkable market value and utilization prospects.

Clay-supported carbon nanotubes (Cs-CNTs) were used as novel nanofillers to improve the thermal and mechanical properties of a polymer. Cs-CNT/poly (vinyl alcohol) (PVA) nanocomposite films were successfully fabricated, and their relative properties were investigated by using differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Experimental results showed that the thermal stability and dynamic mechanical properties of PVA were remarkably enhanced by incorporating the Cs-CNTs into PVA matrix. The largest T(g) difference of 14 degrees C was obtained between pure PVA and PVA nanocomposite with 7 wt% Cs-CNTs. Moreover, the storage modulus of PVA was significantly improved by 133% at 50 degrees C, when 7 wt% Cs-CNTs was added to PVA matrix. POLYM. COMPOS., 30:702-707, 2009. (C) 2008 Society of Plastics Engineers

We demonstrate the use of molecular monolayers to enhance the nucleation of electrocatalytically active PtNi alloy nanoparticles onto the multi-walled carbon nanotubes (MWCNTs). After the siloxane was polymerized on the nanotube surfaces, the carbon nanotubes were embedded within the polysiloxane shell with a hydrophilic amino group situated outside. Subsequent deposition of PtNi nanoparticles led to high density of 3–10 nm diameter PtNi alloy nanoparticles uniformly deposited along the length of the carbon nanotubes. The presence of MWCNTs and PtNi in the composite films was confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersion X-ray spectra analysis (EDS). The electrocatalytic activity of the PtNi-modified MWCNT/polysiloxane (PtNi/Si-MWCNT) composite electrode for electro-oxidation of methanol was investigated by cyclic voltammetry (CV), and excellent electrocatalytic activity can be observed.

An effective method was used to make clay exfoliated successfully. This modified clay hybrid (denoted as E-MMT) was directly used as a filler to improve the mechanical properties of the polymer. E-MMT/epoxy nanocomposites were prepared through an in situ polymerization process. It was found that the Vicker's hardness and the impact intensity of nanocomposites increased effectively. Compared with the pristine epoxy, the Vicker's hardness and impact strength of the 1 wt.% E-MMT/epoxy nanocomposites were greatly improved by 36.4% and 110%, respectively. The mechanisms of the significant improvements were also discussed.

A novel chemical method based on ultrasonic assisted polyol synthesis for the fabrication of highly dispersed Pt nanoparticles on multi-walled carbon nanotubes (MWCNTs) was developed. The simple and green method took only about 10 min at ambient temperature. The structure and chemical nature of the resulting Pt/MWCNT composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS). The results showed that the prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt nanoparticles was about 2.8 nm. Electrochemical properties of Pt/MWCNT electrode for methanol oxidation were examined by cyclic voltammetry (CV) and excellent electrocatalytic activities could be observed. The possible formation mechanism of Pt/MWCNTs was also discussed.

In this paper, novel photocatalysts were prepared by PO 4 3− and PO 4 3− /SO 4 2− surface modification of TiO 2 . Photocatalytic activities of these photocatalysts as affected by preparation conditions were studied by examining the degradation of aqueous methylthionine chloride solution. Their properties were measured and compared by XRD, IR and UV. The experimental results indicate that the modification of TiO 2 by PO 4 3− and PO 4 3− –SO 4 2− enhance distinctly its photocatalytic activity, especially the PO 4 3− –SO 4 2− /TiO 2 . The synergistic effect of photocatalytic decomposition and surface acidity of catalyst is observed by optimized the ratio of PO 4 3− and SO 4 2− . Super acidification of TiO 2 increases the absorbance of catalyst in ultraviolet region, and improves distinctly the photocatalytic activity on 365 nm light.

Shallow-depth acoustic reflection profiling survey has been conducted on the Tanlu fault zone in Laizhou Bay. It is found that the Tanlu fault zone is obviously active during the late Quaternary and it is still the dominating structure in this region. The Tanlu fault zone consists of two branches. The KL3 fault of the western branch is composed of several high angle normal faults which had been active during the period from the the latest Pleistocene to early Holocene, dissected by a series of northeast or approximate east-west trending fault which leaped sediment of the late Pleistocene. The Longkou fault of the eastern branch consists of two right-laterally stepped segments. Late Quaternary offsets and growth strata developed along the Tanlu fault zone verify that the fault zone retained active in the latest Pleistocene to the early Holocene. The Anqiu-Juxian fault that passes through the middle of Shandong and corresponds to the Longkou fault is composed of a series of right-laterally stepped segments. The active faults along the eastern branch of the Tanlu fault zone from the Laizhou bay to the north of Anqiu make up a dextral simple shear deformation zone which is characterized by right-lateral strike-slip movement with dip-slip component during the late Quaternary.

Shallow- depth acoustic reflection profiling survey has been conducted offshore of the northern Shandong peninsula, and the late Quaternary offset features of the Penglai-Weihai fault zone are documented from more than ten shallow profiles. The fault zone passes through the offshore area between the Changdao islands and the Dazhudao island, and consists of a group of NW trending faults, which are dominated by normal and reverse slips with strike-slip component. The Penglai-Weihai fault zone is characterized by the obvious Quaternary activity, which can be divided by the Taocun-Dongdoushan fault in the North Huanghai (Yellow Sea) into two segments, the Changdao-Yantai segment and the Yantai-Weihai segment from west to east, respectively. The western Changdao-Yantai segment is a late Pleistocene active segment, where the uppermost fault points discovered in the survey are buried at more than ~30m bellow the sea bottom, and offset the early to middle late Pleistocene sedimentary layers, and no Holocene offset has been found. The eastern Yantai-Weihai segment is a mid Pleistocene segment on which no late Pleistocene offset has been found. The Penglai-Weihai fault zone is closely related to the occurrence of history strong earthquakes and modern small earthquakes, among them the 1548 Bohai strait Ms7 earthquake occurred on its western segment and the 1948 Weihai Ms6 earthquake on its east segment. The intersection regions of the Penglai-Weihai fault zone with NE striking fault zones are considered to be the likely places for the future medium to strong earthquakes.

A nonlinear magnitude frequency equation has been derived in this paper on the assumption that all seismicity systems hold fractal characteristics, and according to the differences of relevant coefficients in the equation, seismicity systems are classified into two types: type I, the whole earthquake activity is controlled by only one great unified system; type II, the whole earthquake activity is controlled by more than one great system. One type of seismicity system may convert to the other type, generally. For example, a type I system will change to a type II system prior to the occurrence of a strong earthquake in North China. This change can be regarded as an index for earthquake trend estimation. In addition, the difference between b value in nonlinear magnitude frequency equation and that in linear equation and the term dΔM related to the coefficients of nonlinear terms obtained in this paper are proved to be a pair of available parameters for medium short term earthquake prediction.

Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10-20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north-south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present-day Tibetan Plateau, deformed, and its north-south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since ~15 Ma and a less precisely dated change in orientation of crustal shortening since ~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE-SSW in northern Tibet to more NE-SW and even ENE-WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation. Key Points The north-south limits of Tibet were set by lateral variations in strength Roughly 15 million years ago, deformation of NE Tibet accelerated Since 20-15 million years ago, the orientation of shortening rotated eastward ©2013. American Geophysical Union. All Rights Reserved.

Structure and association of asphaltenes from coal direct hydroliquefaction were studied by fluorescence spectrometry and UV-Vis absorption spectrometry in this paper. The results indicate that asphaltene is aromatic mixtures mainly containing naphthalene nucleus and shows strong fluorescent characteristic. The forming of exciplex between asphaltene and solvent results in the red shift of fluorescence peak and fluorescence quenching of asphaltene that increases with the polarity and electron acceptability. The self-aggregation of asphaltene is formed by non-covalent bond interaction, so that the asphaltene liquefied at higher temperture that shows high aromaticity has stronger association than that liquefied at lower temperature. Aggregation of asphaltene has been found to be a gradual process, in which there is no critical aggregation constant observed, and the inflection point of the plot of apparent fluorescence intensity as a function of asphaltene concentration varies with the excitation wavelength.

Ginsenoside, the major active component in Panax ginseng, which has been used in traditional Chinese medicine, contains a series of derivatives of the triterpene dammarane being attached by some sugar moieties. To clarify the relationship between the structure of ginsenoside and its properties, 11 individual ginsenosides, along with the central structures of ginsenoside, protopanaxadiol and protopanaxatriol, are used in 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) induced hemolysis of human erythrocytes, a good experimental model to research free radical induced membrane damage and to evaluate the antioxidative or prooxidative activities of various antioxidants conveniently. It is found that the central structures of ginsenosides, either protopanaxadiol or protopanaxatriol, play a prooxidative role in AAPH-induced hemolysis of erythrocytes. As to the individual ginsenoside, if there are no sugar moieties attached to the 20-position of the triterpene dammarane, the ginsenoside acts as a prooxidant, that is, Rg3, Rh2, and Rg2. A glucose attached to the 6-position instead of the 20-position sugar moieties can make the ginsenoside an antioxidant, that is, Rh1. The antioxidants among ginsenosides follow two different mechanisms that can be expressed mathematically by the Boltzmann equation, that is, Rc and Rb1, and a polynomial equation, that is, Re, Rd, R1, Rg1, Rb3, and Rh1. The orders of antioxidative ability are Rc > Rb1 and Re > Rd > R1 > Rg1 > Rb3 > Rh1, respectively.

Many studies have focused on the free-radical-initiated peroxidation of membrane lipid, which is associated with a variety of pathological events. Panax ginseng is used in traditional Chinese medicine to enhance stamina and capacity to deal with fatigue and physical stress. Many reports have been devoted to the effects of ginsenosides, the major active components in P. ginseng, on the lipid metabolism, immune function and cardiovascular system. The results, however, are usually contradictory since the usage of mixture of ginsenosides cannot identify the function of every individual ginsenosides on the experimental system. On the other hand, every individual ginsenosides is not compared under the same experimental condition. These facts motivate us to evaluate the antioxidant effect of various individual ginsenosides on the experimental system of free-radical-initiated peroxidation: the hemolysis of human erythrocyte induced thermally by water-soluble initiator, 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). The inhibitory concentration of 50% inhibition (IC(50)) of AAPH-induced hemolysis of the erythrocyte has been studied firstly and found that the order of IC(50) is Rb3 - Rb1Rg2ReRg1 - RcRh1R1. Rb1, Rc and Rg2, as antioxidants, can prolong the lag time of hemolysis. Contrarily, Rg3, Rd and Rh1, together with high concentration of Rb3, Rg1 and Rh2, function as prooxidants to accelerate AAPH-induced hemolysis. The addition of Re does not influence the lag time of hemolysis. The R1 with the concentration ranging from 10 to 20 microM decreases the lag time of hemolysis. These results suggest that there is a mutual interaction that existed in the molecule of ginsenosides since the difference of the structure of ginsenosides is only due to the connective position and type of sugar moieties to the ring of a triterpene dammarane. Moreover, the synergistic antioxidative properties of various individual ginsenosides with alpha-tocopherol (TOH) are also discussed, and it was found that the order of synergistic antioxidative properties with TOH is Rb1RcReRh1R1Rg2Rb3. Rg3, Rd and Rh2, however, act as synergistic prooxidants in the above experimental system. Rg1 does not show any synergistic antioxidative property. Although the antioxidative and prooxidative mechanism of various ginsenosides with or without TOH in AAPH-induced hemolysis of human erythrocytes will be further studied in detail, this information may be useful in the clinical usage of ginsenosides.